1. Technical Field of the Invention
The present invention relates to a production method for deburring die for castings utilizing EDM (electric discharge machining), and more particularly to a production method for deburring die for castings utilizing EDM wherein a prototype of castings is directly utilized as an electrode of an EDM apparatus.
2. Related Arts
Conventionally, a deburring die has been produced in various methods. The deburring die, for example, may be produced by a primitive method comprising the steps of taking measurements of a prototype, storing the measurements in a computer, mechanically working die pieces by wire-cutting, cutting, grinding, or the like, based on the stored measurements, and assembling the die pieces into whole bodies of upper and lower dies. Alternatively, an electroforming method may be employed, which comprises the steps of forming a prototype from a material such as plaster, plastics and the like by the use of dies, copper-plating the thus formed prototype, and subjecting the copper-plated prototype to the electric discharge machining so as to produce the deburring dies. Such deburring dies are primarily used for the production of masks, phonograph records and the like. However, these methods require the prevention of reproduction of scars, cracks and the like produced in the prototype. Additionally, in the case of a prototype formed of a plastic material, the production process is complicated because a preprocessing such as sensitization of the surface of the prototype is required.
The applicant has filed several applications for solving the above problems. Of these, a simple method entitled "a Production Method for Deburring Die for Castings Utilizing EDM" has been disclosed in Japanese Unexamined Patent Publication No. Hei-1(1989)-115522. The gist of the above-mentioned method resides in that a prototype is used as an electrode of an EDM apparatus and a machining gap is defined between the prototype as an electrode and a lower or upper deburring die member and controlled by regulating the descending speed of the prototype while a pulse voltage is applied between the prototype as an electrode and the lower or upper deburring die member for electric discharge machining.
Conventional production methods involve difficulty in taking precise measurements of the prototype. It is particularly difficult to take precise measurements on castings having a specific three-dimensional configuration. Furthermore, the production of dies for such castings requires a highly skilled marking operation as well as great amounts of time and effort. In addition, the electroforming method suffers difficult electro-deposition and complicated works.
The production method as disclosed in the Japanese Unexamined Patent Publication No. Hei-1(1989)-115522 features the direct utilization of the prototype as the electrode. Unfortunately, the prototype will wear and therefore, a lower model die so produced tends to contain dimensional errors, even if such errors are quite small. Accordingly, reading the dimensions of the lower model die with errors gives imprecise measurement values, even if such errors are quite small. If a lower deburring die is produced based on such imprecise values, the resultant die naturally fails to be precisely dimensioned. In some cases, the production of the deburring die may require several prototypes which must be frequently changed in the production process, which is cumbersome.